Ozone having strong oxidation power has been conventionally used in various fields for the purpose of, for example, sterilization, deodorization, decolorization, removal of organic substances, removal of hazardous substances, and synthesis of chemical substances.
A photochemical reaction method using ultraviolet light, for example, has been known as one of methods for industrially generating ozone (O3). In this photochemical reaction method, a source gas containing oxygen (O2) is irradiated with ultraviolet light emitted from an ultraviolet light source such as an ultraviolet lamp including a discharge space in an arc tube. This causes the oxygen in the source gas to absorb the ultraviolet light, thereby causing an ozone generating reaction to generate ozone. Advantageously in such a photochemical reaction method, no nitrogen oxide (NOx) as in a silent discharge method, for example, is generated even when a gas containing oxygen and nitrogen is used as a source gas. Moreover, since discharge occurs only in the discharge space in the arc tube, no dust attributable to an electrode is mixed into an ozone-containing gas containing the generated ozone.
In the photochemical reaction method, a low-pressure mercury lamp is generally employed as an ultraviolet light source (see Patent Literature 1, for example).
Patent Literature 1 discloses an ozone generator having a configuration in which a rod-shaped low-pressure mercury lamp is disposed inside a gas flow channel forming member through which a source gas containing oxygen flows, i.e., in a gas flow channel.
The ozone generator that employs the low-pressure mercury lamp as an ultraviolet light source, however, has the following problem.
Typical wavelengths of light emitted from the low-pressure mercury lamp are 185 nm and 254 nm. The wavelength of 185 nm is an ozone generating wavelength, whereas the wavelength of 254 nm is an ozone decomposition wavelength. Thus, when the low-pressure mercury lamp is employed as an ultraviolet light source, an ozone generating reaction and an ozone decomposition reaction occur at the same time. Furthermore, an oxygen atom (O) generated by the ozone decomposition reaction reacts with ozone, thus reducing the amount of ozone. Therefore, no efficient ozone generation can be expected.
To address such a problem, the use of an excimer lamp that emits light containing much ozone generating wavelength as an ultraviolet light source has been proposed in recent years (see Patent Literature 2, for example).
Patent Literature 2 discloses an ozone generator having a configuration in which a gas flow channel forming member made of an ultraviolet transmitting material and having a double-tube structure is disposed so as to surround a rod-shaped excimer lamp. In this ozone generator, a source gas supplied to the gas flow channel forming member is in an isolated state so as not to be in contact with an electrode of the excimer lamp. In this ozone generator, a high-frequency emission excimer lamp with a frequency of 1 MHz to 20 MHz is employed as the excimer lamp, and an ultraviolet reflection member is provided on the outer periphery of the gas flow channel forming member. This ozone generator can air-cool the excimer lamp by flowing a refrigerant such as a nitrogen gas through a gap between the excimer lamp and the gas flow channel forming member.